Polymethacrylates (PMA) and olefin copolymers (OCP) are two classes of viscosity additives.
Each of these two classes has advantages and disadvantages which are specific to it. The PMAs make it possible to obtain low-temperature rheological properties which are superior to those of the OCPs; in addition, they affect the pour point of the lubricating bases On the other hand, their thickening effect is inferior to that of the OCPs; because of this, they must be employed in higher concentrations when lubricating formulations are produced
Investigations have therefore been made to combine these two additives into a single one in order to unite the advantages of each of these polymers in a simple manner.
Attempts have been made to produce an additive of this kind, the simplest method consisting in mixing the two polymers, starting with commercially available additives. However, as is indicated by U.S. Pat. No. 4,290,925 and BE Patent No. 870,329 (the latter corresponding to U.S. Pat. Nos. 4,149,984 and 4,229,311), such mixtures are stable over time only when one of the polymers represents less than 5% of the total weight of the polymers This is why more complex methods have been envisaged, such as the grafting of a PMA onto an OCP backbone (BE Patent No. 870,329, U.S. Pat. No. 4,229,311 and U.S. Pat. No. 3,923,930). A more complex technique consists in grafting an OCP with PMA and then employing this copolymer as a compatibilizer to stabilize emulsion mixtures of OCP and of PMA (European Patent No. 193,272 and U.S. Pat. No. 4,290,925).